Method of forming flexible sheets of cured foamed rubber



J. F. MOORE March 19, 1963 METHOD OF FORMING FLEXIBLE SHEETS OF CUREDFOAMED RUBBER Filed 001;. 15, 1959 INVENTQK,

JOHN E mooig BY Arrows/s United States Patent 3,081,496 METHOD OFFORMING FLEXIBLE SHEETS 0F CURED FOAMED RUBBER John F. Moore, 100Hillsdale Ave. W., Toronto, Ontario, Canada, Filed Oct. 15, 1959, Ser.No. 846,748 4 Claims. (Cl. 18-53) This application is acontinuation-in-part of application Serial No. 677,146, filed August 8,1957, and now abandoned.

' This invention relates to a continuous method of forming flexiblesheets of heat cured plastic material. The invention is particularlyapplicable to the production of cavitied sheets of foamed natural orsynthetic rubber such as are used in bed mattresses, upholstery and thelike.

The object of the invention is to provide a continuous method of formingflexible sheets of cured foam rubber economically and efficiently, thesheets being of considerable width andof any desired length. p

The invention will now be described by way of example with reference tothe accompanying drawings in which: 7

FIGURE 1 is a diagrammatic perspective view of apparatus for carryingout the method according to the invention and partly broken away to showdetails of construction; and FIGURE 2 isa detail sectional elevation ona larger scale of part of the surface of the drum shown in FIG- URE 1.

The invention will be described with reference to the manufacture ofcavitied sheets of foam rubber such as are used in bed mattresses andupholstery.

The rubber compound which is used forms no part of the present inventionand its composition will only be described somewhat briefly. Theprincipal raw material used in the manufacture of foam rubber is naturallatex or a mixture of natural and synthetic latices containing about 60%of solids by weight. The alkalinity of the latex is reduced to asuitable value by blowing air over the surface of the latex and thensulphur and other ingredients such as accelerators and anti-oxidants areadded in the form of colloidal dispersions. The resulting mix- 'ture isthen matured by heating for twenty hours at a temperature of 100 F. and'is then cooled to about 70 F. Potassium oleate and/or castor oil soapare added in the desired proportions together with more sulphur andaccelerators. The mixture is then cooled to about 50 F. The resultingmixture is foamed in a conventional foaming machine consisting, forexample, of an agitator in a closed chamber. The mixture is pumped intoone end of the chamber and compressed air is also admitted so that,during agitation, the pressure is maintained at be :tween twenty andforty pounds per 'square inch in the chamber. Just prior to its leavingthe chamber the foamed mixture has added thereto gelling agentsconsisting of dispersions of zinc oxide and sodium silico-fluoride whichare pumped into the chamber near the exit. The prepared foam, which issupported by the soap bubbles formed during foaming and which ishereinafter referred to as soap supported foam, then flows through aflexible tube to the forming apparatus now to be described. The gellingagents used act at room temperatures but their action is accelerated byheat whereby, as described below, the foamed structure can be gelledrapidly before the soap bubbles decay.

Referring now to FIGURE 1, a drum, indicated generally at 10 is mountedfor rotation about a horizontal [axis 11. The drum is provided with endrings 12 each of which carries a flanged rail 13 which, in turn, engageswith a pair of supporting anddriving wheels 14. The

3,081,496 Patented Mar. 19, 1963 pulley 16, belts 17, pulleys 18 andshafts 19 which are supported in trunnions 20. The drum has an outersurface which is provided by an aluminium cylinder indicated at 21 and:has a plurality of outwardly directed projections some-of which areindicated at 22.

Referring now to FIGURE 2, it will be seen that each projection -22 isin the form of a pin having a reduced end 23 which passes through a hole24 in the aluminium cylinder 21. The reduced end 23 on each pin isprovided with a peripheral groove which receives a spring-ring 25. Thepins are mounted on the drum by inserting their reduced ends 23 throughthe holes 24 and then inserting the spring-rings 25 into the grooves tokeep the pins in place. The drum is provided at each end with aperpiher-al rim 26 connected to the end ring 12 by bolts'27. Theperipheral rim 26 may be made either of electrically insulatingmaterial, for example, Bakelite, or of electrically conduc tivematerial. Similarly the pins 22 may either be made of electricallyinsulating material or of electrically conductive material to producedifferent effects as will hereinafter be described. 7 Returning now toFIGURE 1, a tank indicated generally at 28 surrounds the lower portionof the drum 10 :and is filled with water to a level 29 above thehorizontal axis 11 so that approximately three fifths of the peripheralsurface of the drum is immersed in the water. The tank 28 has aframework 30 which supports the trunnions 20 and is provided with anexternal cover 31 and also with a slotted internal cover 32 extendingwithin the drum 10.

Mounted adjacent to the uppermost portion of the outer peripheralsurface of the drum 10 is a nozzle 33. Means consisting of a slideway 34and a lead screw 35 are provided to reciprocate the nozzle 33longitudinally of the drum across the Whole length of the dmm wherebyrubber delivered from the nozzle is deposited over the whole length ofthe drum. Side guards 36 are provided to prevent the depositedrubberfromoverflowing from the ends of the drum and a Water-cooled scraper 37 isprovided adjacent to the nozzle 33 and has means (not shown) foradjustably spacing it from the surface of the drum by a distance whichdefines the thickness of the sheet produced on the drum. Pipes 38, 39act as water inlets and outlets to the scraper 37. The drum is driven inan anti-clockwise direction as indicated by the arrow X.

- Anti-clockwise of the nozzle 3-3 and the scraper 37 is arranged aheating electrode 40 spaced from the surface wheels 14 are driven by anelectric motor 15 through a of the drum and connected to one terminal ofa source of high frequency voltage, indicated diagrammatically at 40a.The electrode is supported in aninsulated manner from the tank 28 by anarm 41. A roller 42 is mounted in ball bearings 43 adjacent to the pointof entry of the drum into the tank and is rotated by contact with therubber to smooth the surface of the rubber sheet before it enters thetank. Screw jacks 44 are provided to adjust the position of the roller42.

Mounted above the drum and clockwise of the nozzle 33 are three fansindicated at 45 driven by electric motors 46 to force cooling airtowards the surface of the drum, the fans being mounted on a framework,not shown. Mounted inside the drum are two spray tubes 47, 48 ar rangedto spray cooling water onto the interior surface of the drum. The tubes47, 48 are supplied with water from a source (not shown) via a tube 49.Arranged adjacent to the point of exit of the drum from the tank is atake-oft roller 50 and a support roller .51. The roller 59 is mounted inbearings 52 and the roller 51 is mounted in trunnions 53. A lowersqueeze roller 54 is mounted in brackets,55 which also carry an uppersqueeze roller 56 on an arm 57. A set screw 58 is provided to adjust thenip between the rollers 56 and 57. A

on a shaft 61 driven by the motor 15 and rotated to agitate the water inthe tank. The other terminal of the source of high frequency is groundedto the tank 28 which is in electrical contact with the aluminiumcylinder 21, the outside surface of the drum, and also with the pins 22,and/or rim 26, when made of electrically conductive material, throughthe Water and the driving wheels 14.

The operation of the apparatus is as follows:

Foam rubber mix, prepared as described above, is delivered from afoaming machine to the nozzle 33 along a flexible tube 63 and isdeposited on to the uppermost portion of the outer surface of the drumwhich provides a former for supporting the rubber. The material buildsup behind the scraper 37 into a bank indicated at 64 and rotation of thedrum in the direction of the arrow X moves a layer of the depositedrubber under the scraper 37, the layer is of sufficient depth to coverthe pins 22 and has a portion overlying the pins. As the rubber passesunder the electrode 40, the high frequency voltage impressed between theelectrode 40 and the aluminium cylinder 21, assuming that the pins 22and rim 26 are of electrically insulating material, causes dielectricheating of the rubber on the portion of the cylinder 22 opposite to theelectrode and raises its temperature to approximately 100 F. If theprojections 22 and the rim 26 are of electrically insulating material,and electrostatic field will be established between the electrode 40 andthe outer surface fthe aluminium cylinder 21 so that the whole thicknessof the rubber will be subjected to the field and its gelling will beuniform throughout its thickness.

On the other hand, if the pins 22 are of electrically conductivematerial while the rim 26 is of electrically insulating material, theelectrostatic field will be set up between the free ends of the pins andthe electrode 40, thus raising the temperature of the portion of thefoam overlying the pins. This overlying portion will thus gel first andthe foam under the overlying portion will gel more slowly by virtue ofthe gelling agents incorporated in the foam mix as described above. Theaccelerated gelling of the overlying portion will stabilize the foam onthe drum preventing substantial movement of the foam relative to thedrum surface.

When the rim 26 is made of electrically insulating material, it does notmodify the electrostatic field established between the electrode and thesurface of the cylinder, if the pins 22 are of insulating material, orbetween the ends of the pins 22 when the latter are made of electricallyconductive material. If, however, the rim 26 is made of electricallyconductive material, the electrostatic field will be established betweenthe electrode and the rim in the vicinity of the rim. At a shortdistance from such a rim, the electrostatic field will be substantiallythe same as with a rim of insulating material but the depth of the foamwithin the electrostatic field, and heated dielectrically thereby,becomes less the nearer the foam is to the rim and is zero at the rim.Under some circumstances, this lack of rapid gelling is acceptable.

At the temperature of 100 F. gelation of the mix is accomplished in oneor two minutes. This comparatively rapid gelation is such that therubber is gelled before the foam structure in the rubber has had time tobreak down and so that a very fine foamed structure is attained in therubber and the rubber is stabilized relatively to the drum. Whenelectrically conductive pins 22 are used the underlying layer of foammay take about minutes to gel but the foam is prevented from flowing bythe pins 22 and by the previously gelled overlying portion of the foam.As the drum rotates further, the deposited rubber layer has its outersurface smoothed by the roller 42 and then passes into the tank 28 andthen into the hot water in the tank.

The water in the tank is maintained at about 210 F. by the admission ofsteam through the pipe 59 and as the deposited material passes throughthe tank it is cured by the hot water in about 15 minutes. As the rubberis cured, it tends to bake onto the outer surface of the drum, but theabundance of water in the tank and the period of time that the rubberand the drum surface are immersed therein, serves the additional purposeof dissolving the adhesive bond between the cured rubber and the drum sothat the cured rubber may be easily removed from the drum.

Moreover, the water tends to support the rubber in contact with theundersurface of the drum, since the apparent weight of the rubber whenimmersed is less than its actual weight by an amount equal to the weightof the water displaced.

Gelled, but uncured foam rubber has very little inherent strength, butthe lift given to the foam rubber by the water is sufficient to preventthe sheet from breaking while it is on the underside of the drum. Forexample, a piece of foam rubber in hot water Will float with its uppersurface just touching the water surface so that the rubber isweightless. During curing there is a shrinkage of about 3% and this alsohelps to keep the foam sheet in contact with the drum. It is thusunnecessary to provide belts or the like to maintain the rubber incontact with the underside of the drum.

A further advantage of the invention is that it is unnecessary to uselubricants between the rubber and the drum if the liquid of the curingbath is such that it will dissolve the adhesive bond formed as therubber bakes on to the former. Lubricants may, however, be used whenmaking cavitied sheets of foam rubber since the foam is stabilized onthe drum by gelation and the pins 22. However, when uncavitied sheets offoam rubber are being made, lubricants should not be used since the foamis stabilized on the drum by being bonded to the surface thereof duringgelation.

Further rotation of the drum eventually carries the layer of curedrubber out of the Water and then out of the tank. After leaving thetank, the cured rubber is removed from the drum surface and is ledacross the rollers 50 and 51 and between the squeeze rollers 54 and 56.After leaving the squeeze rollers 54 and 56 the rubber is furthersqueezed and dried in a conventional manner which does not form part ofthe invention. A foam rubber product permanently assumes the shape inwhich it is dried and therefore in the method of the invention theproducts will be flat although cured on the curve.

As the drum rotates further, that part of its surface which is noW freeof rubber passes between the water sprays 47, 48 in the interior of thedrum, which cool the metal surface of the cylinder 21, and the fans 45on the exterior of the drum, which cool the pins 22 and rims 26. Thesurface of the drum and the projections and rims are cooled to betweenand F. Further foam rubber is then deposited on this portion of thesurface by the nozzle 33 and the process is continued.

In the embodiment of the invention described, the foam rubber isimmersed in the water in the tank for about 15 minutes and the timeinterval from deposition of the rubber onto the drum until the rubberenters the liquid in the tank is about 5 minutes which is sufiicient togel the underlying portion of the material when electrically conductivepins are used. Similarly, the time interval taken for a point on thedrum to pass from the outlet of the tank to the nozzle is also 5minutes. It will be appreciated that the speed of the drum and the levelof the water in the tank may be adjusted to vary these periods to thedesired value. Thus a lower water level in the tank would provide ashorter curing time whereas increasing the speed of rotation of the drumwould also provide a shorter curing time with the same Water level.

Although the point of deposition of the rubber onto the drum is shown inFIGURE 1 as being at the uppermost point of the drum, the point ofdeposition can be set back in a clockwise direction if desired. Onelimiting feature is that the rubber deposited on the drum must not runin a clockwise direction around the drum. It will be appreciated thatthis limiting feature will in turn be de: termined by the viscosity ofthe rubber and also by the speed of rotation of the drum. The faster thedrum rotates, and the more viscous is the rubber, the further the pointof deposition of the nozzle can be moved in a clockwise direction fromthe uppermost point on the drum. The point of deposition could also beset forward in a counter clockwise direction, the limiting feature beingthat the rubber must begelled before it is inclined at such a slope thatit runs around the drum in an anticlockwise direction. 7

A third limiting feature of the position of the nozzle is that the drumsurface, the projections 22 and the rims a of the foam. Infra-redheating could be used to gel the 3 rubber if desired when thin sectionsare being made. Alternatively, the rubber could be gelled by passing itthrough a chamber containing a steam and air mixture.

The use of pins 22 of electrically conductive material in combinationwith high frequency heating has the fol-- lowing advantages comparedwith the use of pins of electrically insulating material and highfrequency heat (1) The drum and pins are less expensive to manufacturethan if insulating pins are used;

(2) The drum and pins are easier to assemble than if insulating pins areused;

(3) Less high frequency power is required with metal pins since thelayer of rubber gelled is thinner than if insulating pins are used;

(4) Metal pins are generally more robust than pins of electricallyinsulating material such as Bakelite or porcelain; and

(5) Metal pins may be cooled more easily than. electrically insulatingpins.

The advantages of using a rim 26 of electrically conductive material aresimilar to those obtained by using pins of electrically conductivematerial, i.e. less expensive, easier to assemble, more robust andeasier to cool as compared with a rim of electrically insulatingmaterial.

If it is desired to raise the temperature of the curing bath varioussalts, e.g. calcium chloride can be dissolved in the water to raise itsboiling point.

If the apparatus is to be used for the manufacture of mattresses orsimilar discrete articles, axially directed partitions may be arrangedon the drum surface to divide the surface up into a number ofcompartments, the partitions extending outwardly through only part ofthe full depth of the deposited sheet. By this means a plurality ofarticles may be formed joined together by their webs which may be easilysevered. Rounded fillets may be placed at the intersections of thepartitions and the upstanding rims of the drum so that the articles areformed with rounded corners. If desired the surface of the drum could belocally flattened so that the outer face of the product would becrowned.

The apparatus can also be used for the manufacture of composite foamrubber and cloth sheets, the cloth being fed onto the drum in advance ofthe deposition point of the rubber. Alternatively the cloth may be feddown the scraper blade so that the cloth lies on top of the rubber.

Although the invention has been described with refsrence to themanufacture of cavitied sheets of foamed rubber, it will be appreciatedthat if the projections 22 are omitted from the surface of the drum andthe surface of the drum is made imperforate, the apparatus may beoperated to produce plane sheets of foamed rubber in the same manner asthat described for the productionof cavitied sheets.

. It is to be understood that the form of the invention herewith shownand described is to be taken as a preferred example of the same and thatvarious changes in the shape,- size and arrangement of the parts may beresorted to without departing from the spirit of the invention or thescope of the subjoined claims.

What I claim as my invention is:

1. A continuous method of forming a flexible sheet of cured foamedmaterial, having cavities in one face thereof, the material beingselected from the group consisting of natural rubber, synthetic rubbers,mixtures of natural and synthetic rubbers and mixtures of syntheticrubbers, including, the steps of depositing uncured, soap supported,foamed material onto a continuous rigid former to support the material,said material containing a gelling agent whose action is accelerated byheat, and the former having projections thereon to form the cavities;passing the former and deposited material through a heating zone to heatthe material and to cause the gelling agent rapidly to gel the materialand to stabilize it relatively to the former, passing the gelledmaterial and former together through a curing bath of a hot liquid sothat substantially the whole of the volume of the gelled material isimmersed in the liquid, the former being passed through the bath in apath such that, as the material is cured by the liquid, the material issupported against the former by the buoyancy of the material in theliquid; removing the material and the former from the bath; and removingthe cured material from the former.

2. A continuous method of forming a flexible sheet of cured foamedmaterial, having cavities in one face thereof, the material beingselected from the group consisting of natural rubber, synthetic rubbers,mixtures of natural and synthetic rubbers and mixtures of syntheticrubbers, including the steps of continuously depositing uncured, soapsupported, foamed material onto a continuous rigid former to support thematerial, said material containing a gelling agent whose action isaccelerated by heat, and

the former having projections thereon to form the cavities; passing theformer and deposited material through a heating zone to heat thematerial and to cause the gelling agent rapidly to gel the material andto stabilize it relatively to the former, passing the gelled materialand former through a curing bath of a hot liquid so that substantiallythe whole of the volume of the gelled material supported by the formeris immersed in the liquid, the former being passed through the bath inan .arcuate path such that, as the material is cured by the liquid, thematerial is supported against the former by the buoyancy of the materialin the liquid; removing the material and the former from the bath; andremoving the cured material from the former.

3. A continuous method of forming a flexible sheet of cured foamedmaterial having cavities in one face thereof, the material beingselected from the group consisting of natural rubber, synthetic rubbers,mixtures of natural and synthetic rubbers and mixtures of syntheticrubbers, including the steps of depositing uncured, soap supported,foamed material onto a continuous rigid former to support the material,the former having projections to form the cavities and the materialcontaining a gelling agent whose action is accelerated'by heat and beingdeposited on the former in sulficient depth to have a portion overlyingsaid projections; subjecting said overlying portion of the material toheat to cause the gelling agent to rapidly gel said portion thus tostabilize the material relatively to the former; subsequently gellingthe remainder of the material under said overlying portion with thegelling agent; passing the material and the former together through acuring bath of a hot liquid in an arcuate path so that substantially thewhole of the volume of the gelled material supported by the former isimmersed in the liquid, the rigid former being passed through the bathin an arcuate path such that, as the material is cured, it is supportedagainst the former by its buoyancy in the liquid; removing the materialand the former from the bath and removing the cured material from theformer.

4. A continuous method of forming a flexible sheet of cured foamedrubber, said sheet having cavities in one face thereof, comprisingdepositing uncured, soap-supported, foamed rubber latex material onto acontinuous rigid former to provide a sheet of said latex material havingan inner face supported by said former and having a free outer face,said former having projections thereon to form said cavities in theinner face of said sheet; said rubber latex material containing agelling agent whose action is accelerated by heat; passing the formerand deposited material through a heating zone to cause the gelling agentrapidly to gel the material and to stabilize it relatively to theformer; passing the gelled material 20 the material in the water;removing the material and former from the bath; and removing the curedmaterial from the former, the inner face of the material remainingagainst the rigid former throughout the entire gelling and curingoperation.

References Cited in the file of this patent UNITED STATES PATENTS1,528,537 Draemann Mar. 3, 1925 2,308,951 Novotny et al. Jan, 19, 19432,371,155 Czapek Mar. 13, 1 945 2,673,723 Keen Mar. 30, 1954 2,693,006Shigekawa Nov. 2, 1954 2,822,573 Wasniewski et al Feb ll, 1958 2,841,856Gelbman July 8, 1958 FOREIGN PATENTS 466,629 Great Britain June 1, 1937477,911 Great Britain Jan. 10, 1938 OTHER REFERENCES The VanderbiltLatex Handbook, 1954, Winspear, George G. (ed.), published by R. T.Vanderbilt Co., Inc., New York, pp. 215-227.

1. A CONTINUOUS METHOD FOR FORMING A FLEXIBLE SHEET OF CURED FOAMEDMATERIAL, HAVING CAVITIES IN ONE FACE THEREOF, THE MATERIAL BEINGSELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER, SYNTHETIC RUBBERS,MIXTURES OF NATURAL AND SYNTHETIC RUBBERS AND MIXTURES OF SYNTHETICRUBBERS, INCLUDING THE STEPS OF DEPOSITING UNCURED, SOAP SUPPORTED,FOAMED MATERIAL ONTO A CONTINUOUS RIGID FORMER TO SUPPORT THE MATERIAL,SAID MATERIAL CONTAINING A GELLING AGENT WHOSE ACTION IS ACCELERATED BYHEAT, AND THE FORMER HAVING PROJECTIONS THEREON TO FORM THE CAVITIES;PASSING